LONDON — Last week Labour was at the wrong end of one of the most remarkable electoral events in the history of British politics.

The Conservatives won the Copeland by-election, becoming the first ruling party to make a mid-term gain of a comparable size since 1878.

The Tories were jubilant as their candidate Trudy Harrison was announced as the winner in the early hours of Friday morning. The next day Theresa May made the 300 mile-plus trip up to Millom in Copeland to celebrate the "astounding" result.

For Labour, it was a truly miserable affair.

Councillor Gillian Troughton finished more than 2,000 votes behind Harrison despite having all the qualities and life experience to be a big hit with locals. Not even the campaigning nous of Labour's highly-rated elections strategist Andrew Gwynne could rescue the once-safe seat.

So what went wrong for Labour? This week we have spoken to figures within and close to Labour's campaign on the Cumbrian coast to find out what led to the historic defeat.

"I wouldn't say the Tories won it so much as Corbyn lost it"

It's worth noting that Labour's support in Copeland — like in many of its traditional, heartland constituencies — was on the decline long before Jeremy Corbyn was elected leader. Labour's share of the vote has been shrinking since 2001. Since the election of Tony Blair in 1997, Labour's vote share in Copeland has gone from 58% to 42.3% in 2010.

However, if Labour was already a sinking ship in Copeland prior to Corbyn taking over, then his arrival on the scene as party leader has put the ship out of its misery, like a second iceberg to a half-submerged Titanic.

"From the doorstep, it was Corbyn," a source within Labour's ground campaign told us.

"The NHS campaign cut through and would have won it for us with a different leader. Too many long-time Labour voters wouldn't turn out because of him, though they couldn't bear to vote Tory.

"I wouldn't say the Tories won it so much as Corbyn lost it."

They added: "The campaign we ran couldn't have been better, while the Tory ground campaign was virtually non-existent other than in Keswick. Previous Labour voters don't see Corbyn as a leader and don't trust him on nuclear, despite the pro-nuclear position of Gillian and Labour in general. So they stayed at home."

Corbyn's well-documented opposition to the nuclear industry was always going to be a big issue on doorsteps, no matter how much Labour tried to play it down. The Sellafield nuclear power station is Copeland's lifeblood, providing jobs to thousands in an area where most industries that once thrived are now no more than ancient relics.

"It's the power station," the taxi driver who took us to the count on Thursday told us. "Simple as that. The Tories want to keep it open. They are good for this area." Lots more locals who we spoke to about the by-election agreed.

Labour activists believe Corbyn failed to make clear his newfound commitment to nuclear power and the development of an additional site at Moorefields, which once completed is estimated to bring around 20,000 more jobs to the area.

"Corbyn came to Copeland to talk to members and was told to his face that we would lose it because of nuclear, but it took him weeks before he openly stated that he supported Moorside," the source for Labour on the ground added.

"NHS, nuclear and Corbyn were the three big things that came up on the doorstep. Brexit barely registered.

"I honestly thought the result might have been a little closer. But wasn't surprised that we lost."

An activist who has worked for Labour on a number of campaigns, including Copeland, offered a very similar assessment. "With a leader who ran his leadership campaign on a platform against new nuclear, nobody trusted us, and that spread to other parts of the campaign.

"If voters couldn't feel they could trust us on Moorside, could they trust us to save the hospital?"

"Troughton, as a candidate, ticked every box"

That's not to say that campaigning aggressively on the NHS was an unwise move by Labour. Quite the opposite.

The impact of cuts on the local West Moreland Hospital was of great concern for locals. Especially the fate of the maternity unit, which if closed would force pregnant mothers to travel over 40 miles to give birth at a unit in nearby Carlisle. May failed to offer her full support for the threatened unit when she visited prior to the by-election.

View photos

Gillian Troughton Jeremy Corbyn

Danny Lawson PA Wire/PA ImagesBut the NHS is an age-old attack line that although clearly still relevant was not enough to persuade voters to overlook Corbyn's perceived opposition to their area's main employer.

In that sense, the main forces at work in the Copeland by-election effectively went beyond Troughton and the focus of her local campaign.

"Troughton, as a candidate, ticked every box. She's driven ambulances, worked in the hospital, has family that works in Sellafield," the experienced Labour activist told us.

"We selected a candidate who has really strong local links, aired our support for the Moorside development, and focused our campaign on the hospital. In terms of the campaign itself, we did it by the book.

"But, when you have an isolated community like the Cumbrian coast, you can't be seen as being against basically the only major employer in the area.

"It is a shame for her, she is a decent candidate, and under a different leadership team we could well have won. She's probably been let down by the national picture."

"The messaging was ugly"

Even on the NHS, an issue that just about remains within Labour's comfort zone, particularly at a local level, the campaign relied on worn-out messaging and took a dark turn when it said a Tory victory would kill local babies.

Tweet Embed:https://twitter.com/mims/statuses/832144824597889025The gloves are well and truly off in Copeland now. A local mother writes for Labour that Tory NHS cuts will lead to babies dying pic.twitter.com/QIWcrfHNcd

"I would also say that the messaging was ugly. Leaflets and newspaper ads in which the core message boils down to 'vote Labour or babies will die' is pretty ugly, even by the standards of by-elections. That can be off-putting."

It would be wrong to blame Corbyn for all of Labour's woes. After all, issues like the party's collapse in Scotland and painful struggle to appease its traditional support are structural ills that predate his 2015 election.

But for those at the coalface of selling Labour to the country, the causes of their defeat last week could not have been clearer.